Supranormal differential renal function is real but may be pathological: Assessment by (99m)technetium mercaptoacetyltriglycine renal scan of congenital unilateral hydronephrosis

Purpose: It is unclear whether supranormal differential renal function of t he hydronephrotic kidney is real or artifactual. We investigated the effect of clinical and renographic parameters on differential renal function. Materials and Methods: The study included 34 males and 10 females from 1 to 9 months old (median age 2.6 months) with unilateral congenital hydronephr osis. A (99m)technetium (Tc) mercaptoacetyltriglycine (MAG3) scan was perfo rmed, and regions of interest were drawn on the kidneys, and perirenal and lateral backgrounds. Differential renal function was calculated with and wi thout background subtraction at 30-second intervals from 0.5 to 3 minutes a fter injection of Tc-99m-MAG3. The effects of age, sex, obstruction, site a nd size of the hydronephrotic kidney were analyzed using the generalized es timating equations method. Results: There were 11 right and 33 left hydronephrotic kidneys. An obstruc tive renographic pattern was present in 33 cases. The trends of differentia l renal function according to intervals were different between kidneys with and without background subtraction, and differential renal function increa sed significantly as size increased (p <0.05). Differential renal function of the hydronephrotic kidney with an obstructive renographic pattern increa sed with time when perirenal or no background subtraction was applied (p <0 .05). The effects of age, sex or laterality on differential renal function were not significant. Supranormal function (differential renal function 55% or greater) was present regardless of background subtraction methods and m easurement time. Conclusions: Differential renal function is higher in larger hydronephrotic kidney but; function of the kidney with an obstructive pattern is overesti mated on later phases of Tc-99m-MAG3 renal scan, Supranormal differential r enal function is real and may be pathologic since it is prone to occur in l arger obstructive hydronephrotic kidneys.